Electric heater for water tanks



5 Sheets-Sheet l 6. fetter-n25 Inventor- August 3'. Knez.

A. J. KNEZ ELECTRIC HEATER FOR WATER TANKS Filed March 3, 1939 April 1,;1941. A. J. KNEZ 223K151 ELECTRIC HEATER FOR WATER TANKS Filed March 3,1939 5 Sheets-Sheet 2 August 0'. Knez.

0 0 l0 OIL Inventor:

A. J. KNEZ ELECTRIC HEATER FOR wATER'TANKs Filed March 3, 1939 April 1,1941.

3 Sheets-Sheet 3 Aug 5 Inven'tor: usl: U. Knzz fitter-neg,

Patented Apr. 1, 1941 ELECTRIC HEATER. FOR WATER TANKS August .1. Knez,Chicago, 111., assignor to McGraw Electric Company, Elgin,-lll., acorporation of- Delaware Application March 3, 1939, Serial No.:259,511 I3 Claims.

My invention relates to electric heating elements and particularly toheating elements for use on hot water tanks.

.An object of my invention is to provide a relatively simple metalencased electric heating unit 1 particularly applicable for mountingaround water tanks.

Another object of my invention is to provide a totally metaleencasedsemi-flexible electric heating element of relatively small thicknesswhich can be easily and quickly attached to and removed from properoperative water tank.

Another object of my invention is to provide a relatively thin electricheating element adapted tp be clamped around a water tank and embodyingmeans to maintain substantially uniform clamping pressure duringoperation thereof.

Another object of my invention is to provide a tank heating element inwhich the distancebetween the heating resistor and the tank surface isrelatively small and the area of the heat-conducting contact surfacetherebetween is relatively large.

Another object of my invention is to provide a clamp-on electric heatingelement that can be position on a hot modifications of the devicesillustrated, coming within the scope of the appended claims, are to beconsidered a part of my invention.

' In the drawings,

Figure 1 is a central vertical sectional view through a hot water tankhaving my improved electric-heating element mounted thereon, this viewbeing taken on the line 1-1 of Fig. 2,

Fig. 2 is a. horizontal sectional view taken on' the line 2 2 of Fig. 1,

Fig. 3 is a fragmentary enlarged vertical sectional view, taken ontheline 3-3 of Fig. 2. showing, in front elevation, the means forretaining a heater on the tank,

Fig. 4 is a fragmentary enlarged sectional view of a water tank and aheater clamping bolt, taken on the line 4-4-ofFig. 3

Fig. 5 ma fragmentary detail of a part of the heater structure showing aportion cut out for receiving athermostat,

Fig. 6 is a. detail plan view of an electric heater embodying myinvention, before bending,

mounted on any one of a number of tanks'with but slight changes in theclamping means.

Another object of my invention is to provide an encased electric heatingelement of generally band-like shape, in-which the lateral extent of theresistor is appreciably lessthan that of the casing structure. I 7

Still another object of my invention is to provide an electric heatingelement for use on a hot water tank that shall be so constructed andclamped thereon as to tightly engage the outer surface thereof withsubstantially uniform contact pressure thereb'etween over the entireengaging surface.

Yet another object of my invention is to provide a construction for ahot water tank heater which will reduce heat loss in an outwardlydirection to a relatively small amount.

Other objects of my invention will either be pointed out hereinafter inthe course of a description of several forms of heating elements nowpreferred by me or will be evident from such description.

While I have illustrated several forms of an electric heating elementembodying my invention, I desire it to be understood that I do not wishto be limited to the precise details of construction illustrated in thedrawings and described in the specification but that all obvious Pig. '7is a cross-sectional View therethrough, on an enlarged scale, taken onthe line 1-1 of Fig. 6,

Fig. 8 is a view similar to that of Fig. 7, but taken on the line 8-8 ofFig. 6,

Fig. 9 is a fragmentary enlarged sectional view, taken on the line 9-9of Fig. 8, v

Fig. 1013 a detail perspective view of a terminal member,

Fig. 11 is a fragmentary sectionalview, on an enlarged scale, showingthe welded contact between the gib and the casing strip, this view beingtaken on the line 11-11 of Fig. 6,

Fig. 12 is a fragmentary perspective view showing a clamping extensionsecured to a relatively heavy member of T-shape,

Fig. 13 is a fragmentary enlarged plan view, partly in section, showinga single heating element located at one side of the casing assembly,

Fig. 14 is a sectional view therethrough, taken on the line 14-44 ofFig. 13,

Figs. 15 and 16 are views similar to Figs. 13 and 14 but showing thesingle heating element in the middle of the casing assembly,

Fig. 17 is a plan view, on a reduced scale, of the detail shown in Fig.13, but in complete assembly, and I Fig. 18 is a longitudinal sectionalview therethrough, taken on the line I8-i8 of Fig. 1'7.

Referring first to Figs. 1 and 2 of the drawings, I have thereillustrated a hot water tank 21 of the usual kind, provided atits bottomend with a cold water inlet pipe 23 having a battle thereon and with ahot water outlet pipe 25 at its upper end. The tank 2| is surrounded bya layer 2? of a suitable heat insulating material of the kind nowcommonly used for such purposes and I may provide also an outer casing29 of thin sheet metal r properly protect the heat insulating covering2'8. An outer cover 3| and a bottom plate 88 may cc perate with theouter casing 29 to entirely enclose the heat insulating material. Aplurality of supports 35 may be provided in a manner now well known inthe art.

The electric heating element embodying my invention and to behereinafter described in detail is adapted to be clamped tightly againstthe outer surface of the tank and I may use one or more of suchclamped-on heating elements and I have elected to show a hot water tankstructure having an upper and a lower heating element associatedtherewith.

I provide two tunnel structures 87 for the respective heating elementsand these may be made of relatively thin sheet material, of generallychannel shape in lateral section, the inner side of the tunnel beingopen toward the tank itself. The details of construction of this tunnelare already old in the art and for further information in regard to suchstructure reference may be had to Scharf Pat. No. 2,101,691, assigned tothe same assignee as is the present application. The tunnel structurehas an opening in. its outer wall at one part of its periphery and ispreferably provided with a removable cover 39 to permit of access to thetunnel for purposes to be hereinafter set forth.

It may be desirable to individually thermally control the respectivewater heaters and for this purpose I may provide the tank it withinwardly extending tubes 4i adjacent the top and the bottom heaters,secured to the tank in a water-tight manner, each tube having locatedtherein a conventional form of thennal control member Q3. The details ofthe inwardly extending tube and of the thermal control element thereinas well as the details of the control system for the individual or forthe plurality of heating elements constitute no part of my invention.

Referring now to Fig. 6 of the drawings, I have there illustrated anassembled metal encased heating element before the same has been bent toarcuate shape to adapt it for clamping engagement around a circular hotwater tank. The electric heating element 35 includes an initially flatmetal casing strip il which is preferably relatively thin and at leastsemi-flexible. Against one surface of this metal casing strip I locate arelatively thin strip is of electric-insulating material, such as mica,the width of which may be slightly less than the initial width of thestrip il.

An electric heating resistor 58 may be of the form shown in Fig. 9 ofthe drawings from which it will be noted that the resistor comprises aplurality of substantially parallel-spaced straight,

convolutions conected at adjacent ends by rounded end portions all ofthe parts of a resistor lying initially in the same plane. While I haveshown two such resistor elements extending parallel to each other andalong the heating element I do not desire to be limited to this numberbut may use any desired number of such heating resistors.

An outer strip 53 of thin electric-insulating ma-.

terial, such as mica, is located against the outer surface of innerstrip 49 and of the resistor. A thin sheet metal gib whose width issomewhat less than that of the metal casing strip 41 is positionedagainst the outer surface of the outer layer of mica strip 53 and theside edges of the casing strip 41 are bent around and over the sideedges of the gib 55 and in the course of such bending are compresedtightly thereagainst. This construction provides a substantiallyentirely metal encased mica-insulated heating unit.

A terminal structure for each of the two ends of a heating elementincludes a thin fiat metal plate bl extending laterally of the heatingunit, as is shown more particularly in Fig. 9 of the drawings. A metaltube 59 is associated with the plate 5'! and in order to provide forrelatively large engaging surface therebetween I may bend out one ormore bridge portions El from the plate 57 and preferably flatten thetube 5% to permit of forcing it under one or a plurality of such bridges6 i. I preferably return-bend the ends of the individual resistor wires58 substantially as shown in Fig. 9 of the drawings and insert thesereturn-bent ends in the flattened tube 59after which I may subject theplate 57 and the tube at to further pressure to obtain a relativelylarge current carrying area between the wire El and the tube 59 and atthe same time reduce the thickness of the terminal structure. In orderto prevent relative motion between the tube at and the plate 51 I mayweld the two together although this is not essential. A terminal 63having a screw threaded opening therein may be welded to the tube 59 topermit of connecting supply circuit conductors to the respective ends ofthe resistor for the purpose of energizing the heating element. Thisterminal is preferably of non-circular shape in cross section and has anelectric-insulating bushing 62 loosely associated therewith. A lockingbar 66, of thin sheet metal, may have one end spot welded to the gib 55and surround the bushing 62 to hold' the same in place, as shown inFigs. 6 and 11.

All of the work of assembly hereinbefore described is done before theheating unit itself is bent to substantially arcuate shape to adapt itfor clamping against a hot water tank. It is obvious of course that eventhough the thickness of a heating unit of this kind is very small, onthe order of one-eighth inch, there is an appreciable difference betweenthe length of the casing strip dl and of the gib 55 for the sameperipheral extent. It is desired to minimize the relative movement whichmay occur, between the inner and the outer mica strips during bendingand further to prevent relative longitudinal movement of the parts ofthe heating unit during operation thereof when the temperature may varyfrom room temperature to several hundred degrees Fahrenheit. In order tominimize such relative longitudinal movements I prefer to spot weld twoadjacent points or portions of the casing strip ll and of the gib 55 toeachother, a construction which has been shown more particularly inFigs.

6 and 11 where the welds are indicated by numeral 65. In one embodimentof my invention, the glb 55 itself may have a length sufioient tosubstantially completely encircle a tank or the respective end portionsof the gib 55 may have an extra strip 6% secured thereto, structuralmembers 67 of T-shape, being spot welded between the outer ends of thesestrips, as shown more particularly in Figs. 3 and 4. A plurality ofapertures 69 are provided in the respective T-shaped members 61 throughwhich clamping bolts 1| are adapted to extend. In Fig. 3 I haveillustrated the use of three such clamping bolts spaced from each other,the outer clamping bolts being positioned relatively near to the outeredge of the heating unit in order that the clamping pressure created bythe bolts may be made sub stantially uniform over the entire width ofthe clamped-on heating unit.

I provide a relatively heavy coil type compression spring 13 on each 01'the bolts, and i may initially draw up the individual bolts H to such anextent that the spring l3 associated therewith will be fully compressed.However, while I have shown such fully compressed clamping springs, I donot desire to be limited thereto. 1 do however desire to use relativelyheavy springs of coil or of any other suitable shape, so that arelatively large clamping pressure may be exerted to reduce the actualclearance between the inner surface of the casing strip ll and the outersurface of tanlr it to as small a value as may he possible and therebyreduce the thermal reluctance between the engaging suriaces of the metalcasing strip of the heater and of the water tools, as well as tomaintain a substantially uni form pressure therebetween under alloperating conditions,

It is obvious that since the temperature of the heating unit is higherthan that oi the tank, and of the tank contents, when the heating unitis at its operating temperature it will have expanded to a sli htlygreater peripheral length than when it was installed and mounted in acold condition, which is usually at room temperature. The provision of acompression spring associated with the respective clamping halts of atalze -up efiect of the clamping means with ncreased temperature,whereby I am able to maintain the clamping pressure between the heatingand the tools at a suhstantially constant or uniform amount. in otherwords, the reduction oi clarnpin pressure hetween the heating elementand the tonic surface is a rela= tiveiy small amount only, thereby arelatively highly ehicient heat path between the resistor proper and thetank.

I may here point out i may make the es the casing strip ll relativelysmall and i J use relatively thin sheets 69 and r v insulating materialto therein; re= du h of heat-=flow path from the re= sister pro to thetonic which is to he heated is also has the sheet oi reducing thethermal capacity or the assembled heating element.

1 wish to point out further also that I use substantially incompressiblemedia between the clo sing and the tanl: and that the radial thicknessoi the heating unit has heen reduced to a very small amount. t is alsoobvious that the use of an outer clamping gilc, such as is dis closedin. my invention results in tightly holding the terminal members intheir proner operative positions in the assembled heating unit.

It may he well to here point out that certain of the views exaggerate,even in proportion, the thichness oi the heating unit as actually madein practice, which units have been thus far mode with a radial thicknesson the order oi about one-eighth inch.

In order to install one of these heating units in its proper operativeposition in a tunnel til the cover 39 of the tunnel may be removed andsince the heating unit is semi-flexible l find it possible to insert aheating unit into and move it through the tunnel in which it is to belocated, until the two ends of the gib 55 are positioned adjacent to orin substantial register with the opening covered by plate 39. It is thenpossible to insert the bolts H with a spring 18 thereon and to thentighten them up as hereinhetore described.

It is to be understood that terminal leads 1B are connected to therespective terminals 68 and that these terminal leads may extend to asuitable control box ll supported in any desired manner within theopening in the tunnel covered by plate 39.

In case it becomes necessary to replace a heating unit, the cover 39 andthe control her; it may he removed, ai'ter which the bolts it may heloosened and then removed. I have found it easily possible to causeperipheral movement of the heating unit with one end of the silo 55 ledout through the opening of the tunnel, the flexibility oi the unit beingsumcient to permit oi relatively easy and ouiclr removal oi the heatingunit by a peripheral movement thereof relatively to the tank. The somecomments apply with regard to the insertion of a new or repaired heatingunit;

I wish to here point out that l have found it possible to greatly reducethe radial thickness oi the heat insulating material positioned aroundthe tank and at the some time to re= duce the outside temperature onpart of the casing 29 positioned radially outside of one of the heatingelements, thereby indicating that an electric heating unit of the hindembodied in my invention provides a high eficien y thermal heatsdow pathto the outer surface oi tank, the loss of heat radially out rally fromthe unit, in any manner, greatly re duced.

particularly to ings, l have there illustrated heroine it is maderelatively vii vlded with a recess 79 to. that may clear the thermos nowto Figs. t have ere shown several inclusive. Referring for historic i l,have there illustrated a I 80 ooonerating with glie 83 entirely enclosea heating element two strips 85 oi electric insulating n v as inica,having a heating resists therehetween which resistor may a rnlity oioarallel-extending screed cenvolut connected by integral end nortions, tthat the resistor is not to he won sheet oi mice but is formed to th in13 md is then located lost,

mica sheets 85. The casing strip Bi portions bent over and around theoils 88 substantially the same manner as heretofore been set forth inconnection with the heating ele= merit shown in Figs. 6 and 7.

In tl'iis case however the heating resistor: does not extend oversubstantially the entire width of the casing but extends over only anortion thereof. The rest of the lateral space within the cashier istaken up by a spacing strip 89, pref= erahly of heat conducting metal,the thickness oi which is substantially that of the resistor ill and thetwo mica sheets 85.

The terminal construction may he suhstantiel= iv the same as thathereinbefore descrimd for the heating unit shown in Fig. 6, and as shownin Fig. 10.

Referring now to Figs. 15 and lo, I have there illustrated a slightlydifierent term of heating element including a thin sheet metal casing 99and a glh 93 having a heating element ineither in cased therein whichelement includes two relatively thin sheets 95 of electric insulatingmaterial such as mica and a heating resistor 97] located therebetween.The shape of this resistor ii? is substantially the same as has alreadybeen hereinbeiore described. In this modification I locate the insulatedheating element substantially along the middle of the width of theheating unit and provide a pair of filler or spacer strips 95, one ateach side of the heating unit. In all other respects this heating unitis substan tially the same as has already been described in connectionith Figs. 13 and l may point out that I have found it possible togreatly reduce the lateral width of the heating element, making it onlya fraction of the width of the casing, without increasing the watts persquare inch provided by the heating unit to be an unduly large amount.Tbeprovision oi either one filler strip 89 or of two filler strips as(which, as noted above, may be made of heat-conducting material) makesit sossible to return a relatively large proportion of the heat whichmight otherwise be radiated away from. the outside surface of theheating element to the tank and l find it possible to distribute theheat generated by the resistors 5371 or @li over substantially theentire width of the heating unit Figs. 1? and it sliotv another elementof my invention which may. briefly be described as follows: A heatingelement Hill of the type shown it, 18 or 15 that is consisting only of aa site of substantially the same length as the casing and tlte insulatesheating resister enclosed thereby has a constant length.

Means are goroviclecl whereby I am able to adapt a heating element ofconstant length foruse on the extensions sea, and a terminal member N19of structural shape (here shown as of T-shape) through which terminalmembers the clamping bolts it are adapted to extend.

I have found that a heating unit oi the kind shown in Figs. 13, 1t,- 17and 18 provides a me 13/ eficient construction using relatively thinstrips oi sheet metal which give the desired flexibility while at thesame time the auxiliary end portions loll provide suflicient strength sothat I am enabled. to use relatively heavy clamp ing bolts ll andrelatively heavy springs l8 whereby E find it possible to maintain arelatively low external temperature of the encased heating unitirrespective oi the slight increase in length of the heating unitbecause of rise oi temperature in operation.

I may point out that l have made tests oi such a clamp on a heaterwithout using the equalizing springs l3 and mid th&$&ftl? some time ofoperation, the temperature of the heater itself is several hundreddegrees higher than is the case when the springs 713 are used.

l claim as my invention:

1. A metal encasecl band-like electric heating unit comprising a metalcasing, an insulated heating element in said casing of aopreclablvlesser width than saicl cosine; anrl at least one filler strip ofsubstantially the same thickness as is the insulated heating element atone aisle of said insulated heating element;

2. A metal encased bancldilse electric heating unit comprising a metalcasing, an insulated heating element. in said casing of appreciablylesser width than said casing and at least one heat conducting fillerstrip of substantially the same thickness as is the insulated heatingelement at one side of saiol insulated heating ele= ment.

3. A metal encased bancldiize electric heating unit comprising a metalcasing, an insulated electric heating element in salcl casing at oneside thereof anE having a vviclth wines is a fraction only of the widthof the casing and a beat con-= ducting filler strip of substantiallz:the same thickness as that of the insulated heating element adjacent theother side of the casing and

